The present invention concerns a method and a device related to separating liquid from liquid-containing compressed gas in a two-stage liquid separator.
When separating liquid from liquid-containing compressed gas, as for example compressed in a liquid injected screw compressor, a two-stage method is frequently used. The compressed gas is in this method introduced into a first separator stage comprising a cyclone separator, where 90% or more of the liquid is separated. The separated liquid is collected below the cyclone separator. The compressed gas is then conducted to a second separator stage, comprising a filter, for separation of substantially all the remaining liquid.
In order to make maintenance of the compressor, which is supplied with injection liquid from the pressurized liquid separator, possible, the pressure in the liquid separator is lowered when the compressor is stopped. Since the liquid separated and collected in the liquid separator contains a large amount of very small gas bubbles under pressure and which only slowly leave the liquid, a considerable expansion of the liquid-gas mixture is obtained when the pressure is lowered. There is a great risk at this moment that hot liquid, around 100.degree. C., is ejected through the pressure decreasing valve. Furthermore, there is an even greater risk that the filter of the second stage is filled with liquid, with the result that a completely unacceptable amount of liquid is carried along with the compressed gas when the compressor is restarted. Since the volume of the gas bubbles is inversely proportional to the pressure, the above mentioned problem increases when the delivered pressure of the gas is increased.